But the spread of Linux could be hurt by another group--and ironically, it's the free-software proponents themselves.

For months, in secret, the Free Software Foundation, a Boston-based group that controls the licensing process for Linux and other "free" programs, has been making threats to
Cisco Systems
and
Broadcom
over a networking router that runs the Linux operating system.

The router is made by Linksys, a company Cisco acquired in June. It lets you hook computers together on a wireless Wi-Fi network, employing a high-speed standard called 802.11g. Aimed at home users, the $129 device has been a smash hit, selling 400,000 units in the first quarter of this year alone.

But now there's a problem. The Linux software in the router is distributed under the GNU General Public License (GPL), which the Free Software Foundation created in 1991.

Under the license, if you distribute GPL software in a product, you must also distribute the software's source code. And not just the GPL code, but also the code for any "derivative works" you've created--even if publishing that code means anyone can now make a knockoff of your product.

Not great news if you're Cisco, which paid $500 million for Linksys. In Cisco's case, it's even trickier, because the disputed code resides on chips that Linksys buys from Broadcom. So now Cisco is caught between the Free Software Foundation and one of its big suppliers.

For several months, officials from the Free Software Foundation have been quietly pushing Cisco and Broadcom for a resolution. According to Free Software Foundation Executive Director
Bradley
Kuhn
Bradley Kuhn
, the foundation is demanding that Cisco and Broadcom either a) rip out all the Linux code in the router and use some other operating system, or b) make their code available to the entire world.

And if they balk? Kuhn raises the threat of legal action. "We defend the rights protected by the GPL license," he says. "We have legal teeth, so if someone does not share and share alike, we can make them obey the rules."

The legal teeth belong to Eben Moglen, a Columbia Law School professor who acts as pro bono counsel for the foundation. Moglen says his chats with Cisco have been friendly, and he believes the matter will be settled without a court fight. Cisco and Broadcom wouldn't comment.

The dispute, which was leaked to an Internet message board, offers a rare peek into the dark side of the free software movement--a view that contrasts with the movement's usual public image of happy software proles linking arms and singing the "Internationale" while freely sharing the fruits of their code-writing labor.

In fact, the Free Software Foundation runs a lot of these "enforcement actions." There are 30 to 40 going on right now, and there were 50 last year, Kuhn says. There have been hundreds since 1991, when the current version of the GPL was published, he says. Tracking down bad guys has become such a big operation that the Free Software Foundation has created a so-called Compliance Lab to snoop out violators and bust them.

Who pays for this? The 12-employee Free Software Foundation has limited resources. So it seeks donations. And sometimes it collects money from companies it has busted.

Last year, the foundation alleged that
OpenTV
, a San Francisco company that ships a set-top box containing Linux, was violating the GPL. The drama took months to resolve and ended with OpenTV writing a check for $65,000 to the Free Software Foundation. "They paid us a very substantial payment for our time and trouble," Moglen says.

Sometimes it's the other way around--the foundation gets paid by private companies for whom it acts as a sort of hired enforcer. Last year a Swedish software company called
mySQL
asked for help resolving a dispute with
NuSphere
, a subsidiary of
Progress Software
. The companies had made a deal to work on software that would include mySQL's GPL-licensed database program. A dispute arose over contract issues, and also over the GPL, which mySQL claimed NuSphere had violated. In the end, Progress resolved the matter by walking away from the partnership.

Afterward, mySQL made a $25,000 donation to the Free Software Foundation. Was this payback? "I won't say that," says
Marten
Mickos
Marten Mickos
, chief executive of mySQL. "But of course, why would we give them money if not as a sign of gratitude?"

The mySQL versus NuSphere squabble demonstrates another risk: These disputes might scare companies away from using open source software.
Joseph
Alsop
Joseph Alsop
, chief executive of Progress, reckons the fiasco with mySQL cost his company $10 million in lost development and marketing work. Now he says he is cautious about working with GPL software. Instead, Progress uses an open source database program distributed under the less onerous Berkeley Software Distribution license.

In some ways, these Free Software Foundation "enforcement actions" can be more dangerous than a typical copyright spat, because usually copyright holders seek money--say, royalties on the product that infringing companies are selling. But the Free Software Foundation doesn't want royalties--it wants you to burn down your house, or at the very least share it with cloners.

Or maybe, as some suggest, the foundation wants GPL-covered code to creep into commercial products so it can use GPL to force open those products. Kuhn says that's nuts--"pure propaganda rhetoric." But he concedes that his foundation hates the way companies like
Oracle
and
Microsoft
generate billions of dollars by selling software licenses. "We'd like people to stop selling proprietary software. It's bad for the world," Kuhn says.

So far, none of the Free Software Foundation's targets have decided it is bad for the world and gone to court. This despite the fact that the foundation has $750,000 in the bank and one lawyer who works for free, part time, when he's not teaching classes at Columbia University.

Will Cisco and Broadcom be the first? Probably they'll decide, like everyone else, that it's cheaper to settle than to fight.